Influence of soil humic acid and fulvic acid on sorption of thorium(IV) on MX-80 bentonite

Sorption and desorption of radiocobalt on montmorillonite—Effects of pH, ionic strength and fulvic acid

Humic substances and clay minerals have been studied extensively in radioactive waste management. In our research, the sorption and desorption of radiocobalt on montmorillonite in the presence and absence of fulvic acid as a function of pH and ionic strength were investigated under ambient conditions by using batch techniques. The results indicate that the sorption of cobalt is strongly dependent on pH values and independent of ionic strength. Surface complexation rather than cation exchange is considered as the main mechanism of cobalt sorption to montmorillonite. The presence of fulvic acid enhances cobalt sorption obviously at pH values<8. The desorption behavior changes of surface-sorbed cobalt from montmorillonite were studied by decreasing pH values and the solution cobalt concentrations independently. The results indicated that the sorption of cobalt on montmorillonite is irreversible.

Sorption–desorption of Th(IV) on attapulgite: Effects of pH, ionic strength and temperature

The sorption of Th(IV) on attapulgite was studied as a function of pH, ionic strength, temperature, attapulgite contents and Th(IV) concentrations under ambient conditions using a batch technique. The results indicated that sorption of Th(IV) on attapulgite was strongly affected by pH values, and weakly dependent on ionic strength. Sorption of Th(IV) was dominated by surface complexation, although ion exchange also contributed to this sorption. Sorption of Th(IV) increased with increasing temperature of the system. Enthalpy (DeltaH(0)), entropy (DeltaS(0)) and Gibbs free energy (DeltaG(0)) were calculated from the temperature-dependent sorption data; the results indicated that the sorption of Th(IV) on attapulgite was a spontaneous process. Sorption-desorption hysteresis indicated that the sorption of Th(IV) was irreversible, and that the Th(VI) adsorbed on attapulgite was difficult to be desorbed from solid to liquid phases.

Sorption of Radiocaesium onto Powdered and Compacted Rectorite Studied by Batch and Capillary Methods

The sorption of radiocaesium onto Na-rectorite as a function of pH value under ambient conditions was studied by batch and capillary methods. The results indicated that the sorption of Cs+ions was dependent on the ionic strength and, to a lesser extent, on the pH value. The distribution coefficients for Cs+ion sorption onto powdered rectorite (as determined via the batch technique) were much higher than those of Cs+ions onto compacted rectorite (as determined by capillary test), thereby suggesting that the sorption of Cs+ions onto rectorite was strongly dependent on the density of rectorite, i.e. the interlaminary space of the compacted rectorite contributes significantly on Cs+ion sorption. The distribution coefficients calculated from theoretical calculations, experimental measurements and the diffusion coefficients of Cs+ions were compared and discussed in detail. The sorption and diffusion mechanisms in compacted rectorite were also discussed.

Effect of soil humic and fulvic acids, pH and ionic strength on Th(IV) sorption to TiO2 nanoparticles

Thorium is considered as a chemical analog of other tetravalent actinides. Herein, the sorption of Th(IV) on TiO(2) in the presence or absence of soil fulvic acid (FA)/humic acid (HA) as a function of pH, ionic strength and FA/HA concentration has been studied by a batch method. The morphology was characterized by scanning electron microscopy (SEM). The results indicate that sorption of Th(IV) on TiO(2) increases from 0% to approximately 94% at pH 1 approximately 4, and then maintains level with increasing pH values. Both FA and HA have a positive effect on Th(IV) sorption at low pH values and the contribution of FA on Th(IV) sorption is rather higher than that of HA at pH<4. The sorption is weakly dependent on the concentration of KNO(3) in solution, but the cations K(+), Na(+) and Li(+) influence Th(IV) sorption more obviously. The batch results indicate that the inner sphere complex formation is formed at bare surfaces or FA/HA-bound TiO(2) particle surfaces. Results of SEM analysis show that the particle sizes of TiO(2), Th-TiO(2) and Th-HA-TiO(2) colloids are quite different. Surface complexation may be considered as the main sorption mechanism.